The field of the present invention is motorcycles and particularly the power train for motorcycles.
Motorcycles of smaller displacement and size, particularly those referred to as motor scooters have been found to advantageously employ V-belt power transmission systems. In such systems, the V-belt drive has often employed variable diameter pulleys. Through the use of such variable diameter pulleys, variable speed ratios may be achieved which vary automatically with the speed of the engine.
Such devices find great utility in the smaller motorcycles because they eliminate control complications for the rider and yet provide a wider range of speeds of the vehicle for a given engine speed range. Because of the simplicity in construction in such systems, variable speed ratio V-belt drives widely adopted for two-wheeled, small, low-priced vehicles requiring a range of operating speeds contain the system generally housed in a case acting as a unitary structure with an engine to prevent dust, mud, and the like from entering the drive system.
In motorcycles of the type employing unitary drive structures, it is important to have relatively compact and lightweight structures. In such compact designs, additional components extending from the lower portion of the structure such as clutch housings, drive train components and the like can protrude objectionably from the silhouette of the vehicle. Such protrusions may, for example, limit the banking angle of the vehicle.
With specific attention to the automatic power transmission system employing a variable speed ratio V-belt drive and the like, a centrifugal clutch is generally employed between the engine and the rear axle. Such a centrifugal clutch prevents the vehicle from being directly engaged when the engine is started and also allows the vehicle to be easily idled and rolled without engine engagement. With centrifugal clutches, the engine is disengaged from the rear axle when the engine rpm's are below a specified value. The engine may then be smoothly engaged by raising the rpm level.
Power train systems employing a clutch acting automatically responsive to engine speed have been placed on a direct line between the axis of the output shaft of the engine and that of the rear axle. This provides a convenient and simple design. Furthermore, where relatively low power must be controlled by the starting clutch, the clutch itself may be realtively small in size and its placement does not result in the clutch interfering with the use of the vehicle. However, with motorcycles of increased power, the starting clutch must be increased in size to meet the power demand. As a result, the clutch portion of such transmission systems can extend objectionably from the side of the vehicle so as to restrict the banking angle, an important driving consideration for motorcycles.
With variable speed ratio V-belt drives, variable diameter pulleys have been employed. When substantial power is directed through the V-belt and frequent cycling through the speed ratios is anticipated, some lubrication of the pulley mechanisms is advantageous. However, the nature of these mechanisms is such that centrifugal force is applied to any lubricant positioned within the actuating mechanisms. Consequently, such lubricant tends to be thrown outwardly to the V-belt. As a result, friction between the pulley or pulleys and the V-belt itself may be reduced by the improperly distributed lubricant. This naturally can result in the loss of smooth drive train operation and the ability to direct full power to the rear wheel of the vehicle.